Reduced subendocardial coronary reserve is a hallmark of left ventricular (LV) hypertrophy. In order to examine whether hemodynamic, as opposed to structural, mechanisms mediated this alteration, the effects of near-maximal vasodilation with adenosine were examined in 10 conscious dogs with left ventricular (LV) hypertrophy (79% increase in LV weight/body weight ratio) induced by aortic banding in puppies. In control dogs, adenosine reduced LV circumferential end-systolic and end-diastolic wall stresses and compressive radial subendocardial wall stress, and the endo/epi ratio decreased from 1.30q0.07 to 0.69q0.05. In dogs with LV hypertrophy, during adenosine LV circumferential end-systolic and end-diastolic wall stresses as well as LV radial subendocardial wall stresses remained elevated, and the endo/epi ratio fell to a lower level, p<0.05, (from 1.22q0.17 to 0.35q0.03). When LV wall stresses during adenosine were reduced in a subgroup of 5 dogs with LV hypertrophy, the endo/epi ratio during adenosine was no longer different from control dogs (0.63q0.11). These data suggest that hemodynamic factors, e.g., compressive forces, are an important component of the reduced subendocardial coronary reserve as opposed to structural alterations, even in the presence of severe LV hypertrophy.